Knowing the chemical composition of hydrocarbons (including but not limited to petroleum oils and asphaltic materials) is critical in applications such as improving the performance of bituminous roadways as well as improving refining and oil production efficiency. Certain embodiments of the inventive technology disclosed herein combine innovative features that provide a comprehensive, automated separation of oils in a manner that has not yet been achieved. This separation provides quantitative information about the relative amounts of several fractions using automated, normal phase chromatography coupled with a novel solubility-based separation of asphaltenes, saturates, naphthenes, aromatics, two subfractions of polars, and three solubility subfractions of asphaltenes. The generated data provide valuable insight into compositional differences between different oils and asphalt binders, the internal chemical changes which occur due to aging or processing, and processing generally. The results can be used in establishing compatibility and for predictive modeling, process control, and improving processing efficiency and yield, inter alia.
Adsorption Chromatography Petroleum Separations:
Separating a material into its constituent parts is often necessary in defining its composition. Separations of oils using normal phase chromatography have been around for several decades. One early version of such type of analysis was developed by Corbett who separated asphalts into saturate, naphthene aromatic, polar aromatic and asphaltene fractions. A similar procedure was described by Jewel et al., in which crude oil or asphalt was separated into saturate, aromatic, resin, and asphaltene (SARA) fractions.
Using well known procedures, before these separations can be performed, the oils are usually first separated into two solubility classes by a gravimetric separation utilizing a low polarity hydrocarbon solvent such as isooctane, pentane, or heptane. The soluble material is by definition called the maltenes or petrolenes. The insoluble material is, by definition, called asphaltenes. The gravimetric asphaltenes/maltenes separation typically takes 24 hours. The chromatographic separation of maltenes takes another day. Certain conventional techniques to separate the maltenes employ gravimetric open-column normal-phase adsorption chromatography using polar stationary phases such as activated silica gel or activated aluminum oxide. If the asphaltenes are to be further separated gravimetrically into two solubility subfractions such as cyclohexane soluble and cyclohexane insoluble, it may take an additional day.
Again, using conventional methods, the maltenes are often separated into three fractions by normal-phase liquid chromatography: saturates, aromatics, and resins/polars. The saturates fractions consist of both linear, branched and naphthenic fully saturated organic molecules of low polarity containing carbon and hydrogen and essentially no hetero-atoms. A molecule in the aromatics fraction contains mainly carbon and hydrogen, possibly some thiophenic sulfur, few if any heteroatoms, and is distinct from the saturate fraction by containing one or more aromatic rings. The resins and asphaltenes fractions both contain many aromatic rings including highly colored pericondensed aromatic structures, with many polar substituents.
Rod Chromatography:
Approaches for SARA separation can be divided into two main groups. The first method that has been widely utilized uses a technique known as thin-layer chromatography (TLC), and when combined with flame ionization detection (FID) becomes semi-automated. This is known as the Iatrocsan method in which capillary thin layer chromatography is conducted with whole oils on silica or alumina rods as a stationary phase, followed by evaporating the elution solvent and then slowly passing the rods through the flame of a flame ionization detector to provide information on the relative amounts of the fractional zones on the rod. The Iatrocsansystem typically elutes the fractions in a sequence of solvents consisting of a linear alkane, cyclohexane, toluene, and dichloromethane:methanol mixtures. However, the Iatrocsan method has severe drawbacks including variable response factors for the different fractions, relatively high amounts of polar compounds retained near the spot location on the TLC rod, and aromatics grouping together to act like resins during separation. The separation is not very repeatable and there is a chronic problem with the strongly adsorbed, asphaltene material which does not migrate up the rod.
Column Chromatography:
The second type of method requires initial precipitation of the asphaltenes by dissolving the sample in an excess of an alkane before further separation of the maltenes into the saturate, aromatic, and resin (SAR) fractions by liquid chromatography. Typical methods for the asphaltene separations are described in ASTM D3279, ASTMD4124 or similar. Many variations of the SAR separation have been developed using amino, cyano, or alumina columns including several automated or semi-automated methods utilizing high performance liquid chromatography (HPLC). Radke et al. described a semi-automated, medium pressure liquid chromatography system to separate maltenes involving three analytical columns and three pre-columns in which the pre-columns had to be re-packed between each injection. Variations for automated separations of the maltenes are typically performed using silica gel derivatized with aminopropyl or cyano functional groups. These typically do not provide fully resolved separations of saturates and aromatics and irreversible adsorption occurs on the columns due to resins and soluble asphaltene-type component molecules. A published version of an HPLC SARA method in the laboratory that uses chemically bonded aminosilane stationary phase for an automated SAR separation of crude oil maltenes has been evaluated and, while the authors claim that it also works on bituminous material, no data were presented to support this assertion and attempts to desorb the most polar fractions of asphalt from their system were unsuccessful, resulting in poor recovery and fouling of the column. Fan and Buckley developed a method that used two aminosilane columns. However, HPLC SARA methods that use chemically bonded aminosilane stationary phase of crude oil maltenes result in fouling of the column because of irreversible adsorption of resins. While their system appears to work well for crude oils, the most polar components of the resins fraction of asphalt became irreversibly bonded to the column. Further, the saturates and aromatics fractions are not completely separated in the Fan and Buckley system. It was evident that a new system was needed for asphalt and heavy oils that performs the SAR separation without fouling the column and that allows full recovery of the resins fraction.
This inventive technology, in embodiments, involves a novel combination of two modes of separation/analysis for hydrocarbons such as, e.g., bitumen and oils, including but not limited to petroleum oils, asphalt, coal liquids and shale oils. In embodiments able to quantify asphaltenic constituents, one component of the combined separation is an automated solubility separation in which asphaltenes are precipitated within a ground polytetrafluoroethylene (PTFE)-packed column. This may be referred to as the AsphalteneDeterminator (AD) separation, and may be as described in U.S. Pat. No. 7,875,464 (perhaps supplemented by disclosure herein). In the second component, the material which is not precipitated may be passed onto a series of adsorption chromatographic columns by normal-phase adsorption liquid chromatography for separation into saturates, aromatics, and resins/polars (SAR) components. The SAR (saturates, asphaltenes and resins) separation may utilize three separate adsorption chromatography columns packed with different sorbents. The first column may be packed with high surface energy, non-porous material to reversibly adsorb the very polar and highly aromatic resins materials to keep them from adsorbing irreversibly on the second (and perhaps the third) column. This packing can include a stationary phase such as glass beads, metal particles, ceramics, or other materials (perhaps generally, non-porous, high surface energy materials). The second column may be packed with a weakly adsorbing stationary phase (e.g., an activity reduced stationary phase) such as deactivated silica or amino or cyano functional groups bonded to a silica matrix. The third column may be a highly active, stationary phase such as activated silica or alumina (perhaps an activity enhanced stationary phase). Flow switching and solvent switching valves may be used to provide a separation sequence in which the highly activated stationary phase is not “activity-reduced” (deactivated) during or between separations, allowing for repeated separations without requiring the stationary phases to be changed or discarded between runs. In a step separate from the adsorption chromatography separation of the maltenes, and perhaps after such adsorption chromatography steps are complete, the precipitated asphaltene material on the PTFE column may be re-dissolved using one or more asphaltene solvents (i.e. solvents able to dissolve at least a portion of the precipitated asphaltenes) to provide a solubility distribution profile of the asphaltene material. The result is a combined automated SAR separation coupled with the automated AD (asphaltene determinator) separation to provide a comprehensive characterization of materials.